Effect of ionic modification of the hydration shell of a charge-neutral radical on its resonance Raman spectrum

The effect of ionic perturbation of the hydration shell on the molecular geometry of a charge-neutral radical has been probed by time-resolved resonance Raman spectroscopy using p-aminophenoxyl radical (H2NC6H4O•) as a model system. The dynamic coupling between the amine scissors and the ring stretching vibrations is found to be greatly enhanced on incorporation of chloride ion in the hydration shell, suggesting an increase in the coplanar character of the radical. This observed ionic effect, not known previously, contrasts with a recent finding that ions have a negligible effect on the hydrogen-bond structure in liquid water.